Electrically-conductive textile fiber

ABSTRACT

FINELY-DIVIDED, ELECTRICALLY-CONDUCTIVE PARTICLES ARE UNIFORMLY SUFFUSED IN A FILAMENTARY POLYMER SUBSTRATE AS AN INDEPENDENT PHASE IN AN ANNULAR REGION LOCATED AT THE PERIPHERY OF THE FILAMENT AND EXTENDING THE ENTIRE LENGTH THEREOF. THE ELECTRICALLY-CONDUCTIVE PARTICLES ARE EMPLOYED IN AN AMOUNT SUFFICIENT TO RENDER THE ELECTRICAL RESISTANCE OF THE FILAMENT NOT MORE THAN ABOUT 10**9 OHMS/CM. THE FILAMENT FIND SPECIAL UTILITY IN THE FABRICATION OF ANTISTATIC FABRICS AND FLOOR COVERINGS.

United States Patent 3,823,035 ELECTRICALLY-CONDUCTIVE TEXTILE FIBERJohn H. Sanders, Deubigh, Va., assignor to Dow Badische Company,Williamsburg, Va.

No Drawing. Filed July 14, 1972, Ser. No. 271,837 Int. Cl. C09c l/44;D02g 3/00 US. Cl. 117226 6 Claims ABSTRACT OF THE DISCLOSUREFinely-divided, electrically-conductive particles are uniformly suffusedin a filamentary polymer substrate as an independent phase in an annularregion located at the periphery of the filament and extending the entirelength thereof. The electrically-conductive particles are employed in anamount sufficient to render the electrical resistance of the filamentnot more than about 10 ohms/cm. The filament finds special utility inthe fabrication of antistatic fabrics and floor coverings.

BACKGROUND OF THE INVENTION Field of the Invention This inventionrelates to textiles in general, and in particular to anelectrically-conductive textile fiber for use in the fabrication ofantistatic fabrics and floor coverings.

Prior Art The accumulation of static electricity as a result of theutilization of fabrics is a phenomenon which has commanded the attentionof the textile industry for some time. The presence of static is a causenot only of annoyance (e.g. items of apparel cling to the body and areattracted to other garments; fine particles of lint and dust areattracted to upholstery fabrics, increasing the frequency of requiredcleaning; one experiences a jolt or shock upon touching a metal doorknobafter walking across a carpet), but also of danger (e.g. the dischargeof static electricity can result in sparks capable of igniting flammablemixtures such as ether/air, which are commonly found in hospitals,especially in operating rooms). All of these effects are accentuated inatmospheres of low relative humidity.

Of the many proposals for preventing the undesirable buildup of staticelectricity, the most satisfactory, with respect to their efficiency andpermanence, appear to be those which comprehend the utilization offibers possessing electrical conductivity (e.g. metal fibers, fiberscoated with electrically-conductive material, or metallic laminatefilaments) in combination with common natural and man-made fibers toproduce a woven, knitted, netted, tufted, or otherwise fabricatedstructure, which readily dissipates the static charges as they aregenerated. Some of the more noteworthy of these methods and structuresmay be found in US. Pats. 2,129,594; 2,714,569; 3,069,746; 3,288,175;3,582,444; 3,582,445; 3,582,448; 3,586,597; and 3,590,570; in Webber,Metal Fibers, Modern Textiles Magazine, May 1966, pp. 7275; and inBelgian Pat. 775,935.

Notwithstanding the efficacy of these and similar expedients, they arefound lacking in certain important aspects, -viz:

The manufacture of metallic fibers of fine denier, expecially in theform of monofilaments, is a difficult and costly operation; and sincesuch fibers are quite dissimilar in character from ordinary textilefibers, problems arise in connection with blending and processing, aswell as in the hand of the products obtained.

Metallic laminate filaments, on the other hand, do not present blendingand processing problems, because of 3,823,035 Patented July 9, 1974their close similarity to ordinary textile fibers, and the hand of theproducts obtained is consequently not objectionable. However, the costof such filaments is high when compared with the natural or man-madefibers with which they are blended.

Textile fiber substrates the surfaces of which have been coated by vapordeposition or electrodeposition, or by the application of adhesivecompositions containing finely divided particles ofelectrically-conductive material, are in some cases less costly thanmetal fibers and/ or metallic laminate filaments, depending upon thenature of the electrically-conductive material employed. However, suchcoatings are often found lacking in cohesion and adhesion and arefrequently too thick to be practicable in some applicationsespeciallywhen the nature of the electrically-conductive particulate matter issuch that a high concentration thereof is required for satisfatcoryconductivity. Economy is achieved, therefore, only through sacrifices indurability of conductivity of the fiber.

The extrusion of powdered synthetic polymer/finelydividedelectrically-conductive material blends into filaments or as extrudedcoatings on a filamentary substrate having the same or a differentpolymeric composition is also well known. Unfortunately, blendsrequiring a high concentration of the electrically-conductive materialare often not readily extruded, if at all, and any filaments andfilamentary coatings which are produced have extremely poor cohesion andadhesion.

SUMMARY OF THE INVENTION Accordingly, it is the primary object of thisinvention to provide a low-cost, yet durable, electrically-conductivefiber which presents no problems in the blending and processing withordinary natural and man-made textile fibers.

This object is achieved, and the disadvantages of the prior art areobviated, by providing an electrically-conductive textile fiber whichcomprises a filamentary polymer substrate having finely-divided,electrically-conductive particles uniformly suffused as a phaseindependent of the polymer substrate in an annular region located at theperiphery of the filament and extending the entire length thereof. Theelectrically-conductive particles are present in an amount sufficient torender the electrical resistance of the textile fiber not more thanabout 10 ohms/cm. In contradistinction to a coating, the annularsuifusion of the present invention is a spreading or diffusion ofelectrically-conductive particles through the fiber substrate itself. Incontradistinction to a filament extruded from an intimate mixture ofpowdered polymer and finely-divided, electrically-conductive material,the suffusion of the present invention is confined to an annulus locatedat the periphery of the filament and extending the entire lengththereof. When the filamentary polymer substrate of the present inventionis of substantially cylindrical configuration, it has been foundespecially advantageous if the annular region of suffusedelectrically-conductive particles extends perpendicularly inwardly fromthe periphery of the filament up to a distance equal to about ,5 theradius of the filament.

The electrically-conductive fiber of the present invention iseconomically produced, has very durable conductive properties, andsubstantially retains the characteristics of the filamentary polymersubstrate, thereby affording a combination of properties unobtainable inthe. prior art. That sufficient conductivity could be achieved withoutsubstantial sacrifice in the characteristics of the filamentary polymersubstrate and without substantial loss of cohesion of polymer in theannular region, is indeed unexpected in view of the prior art.

3 DESCRIPTION OF THE PREFERRED EMBODIMENTS The filamentary polymersubstrate upon which the electrically-conductive textile fiber of thepresent invention is based may be prepared from any of the well-knownfilm or fiber forming polymers, such as cellulosics, polyolefins,polyesters, or polyamides, 'by standard techniques wellknown in the art.A wide range of deniers (viz., from 1 to 100 and above) isadvantageously employed. Monofilaments of polyamides such as 6 nylonhaving a denier of between about and 50 have been found especiallyadvantageous in most apparel and floor covering applications.

The finely-divided, electrically-conductive particles which are suffusedin the filamentary polymer substrate are chosen in the light of theirelectrical conductivity, chemical resistance, weatherability, andresistance to washing, scouring and dyeing treatments, as well aseconomy. Particularly useful are the metallic powders such as silver andbronze, and the electrically-conductive carbon blacks, all of which arereadily available commercially. A wide range of particle sizes has beenfound acceptable. For electrically-conductive carbon black a particlesize of about 20 to 40 m is preferred. The concentration ofelectrically-conductive particles-which is dependent upon the nature andparticle size thereof, as well as the nature of the filamentary polymersubstrate-is chosen so that the electrical resistance of the fiber willbe not more than about ohms/cm., and most advantageously not less thanabout 10 ohms/cm. (If the fiber has an electrical resistance of betweenabout 10 and 10 ohms/cm, it is most advantageously employed in fabricsfor preventing the accumulation of high charges of static electricitywhile presenting no appreciable electrocution hazard.) Whenelectrically-conductive carbon black having a particle size betweenabout 20 and 40 mp. is suffused in a denier monofilament of a polyamidesuch as 6 nylon, for example, a carbon black concentration of betweenabout 2 and percent, based upon the total weight of theelectrically-conductive fiber, is preferred.

The suffusion of finely-divided, electrically-conductive particles inthe filamentary polymer substrate is characterized by the existence of adiscrete, independent phase of electrically-conductive particles,uniformly dispersed in the polymer substrate in an annular regionlocated at the periphery of the filament and extending inwardly alongthe entire length of the filament. When the filamentary polymersubstrate is of substantially cylindrical configura tion, which is verycommon in the art, it has been found of especial advantage if theannular region of suffused electrically-conductive particles extendsperpendicularly inwardly from the periphery of the filament up to adistance equal to about the radius of the filament. Under suchconditions the physical properties of the suffused filamentary substratestill closely approximate those of the unmodified filamentary substratewhile the conductivity thereof has been strikingly increased. Forcross-sectional configurations other than circular (e.g. trilobal,square, rectangular, etc.) the annular region most advantageouslyextends perpendicularly inwardly from the periphery of the filament upto a distance equal to about the radius of a circle inscribed within thecross-sectional perimeter of the filament.

The electrically-conductive textile fiber of the present invention maybe prepared from commercially available filamentary polymer substratesusing special techniques, the most satisfactory of which comprehendapplying to the filamentary polymer substrate a dispersion of thefinely-divided, electrically-conductive material in a liquid which is agood solvent for the substrate but does not react with or dissolve theelectrically-conductive material. A combination of such liquids maybeused if desired. The chosen concentration of electrically-conductivematerial in the solvent system is dependent upon the desired fiberconductivity and is limited by the viscosity of the dispersion.(Dispersions which are either too viscous or not viscous enough aredifficultly applied when certain methods of application are expedient.)

Application of this dispersion to the filamentary substrate may be bypadding, painting, spraying, dipping, rolling, printing, or the like. Ifdesired for viscosity or other purposes, the dispersion may containdissolved polymer of the same nature as that of the substrate, underwhich conditions the annular suffusion terminates imperceptibly in anintegral coating of the same composition. In any event, solvent removalfrom the substrate must be effected before the structural integritythereof is appreciably destroyed. This is conveniently accomplished byvaporization (for volatile solvents) and/or washing with a non-solvent(for non-volatile solvents) after the desired degree of solventpenetration has taken place (esp. up to about of the radius ofsubstantially cylindrical filamentary substrates). By way of example,when filamentary substrates of polyamides such as 6 nylon are employed,the applicable dispersion may be 5 to 15% carbon black in concentratedformic acid, or it may be 5 to 15% carbon black in concentrated sulfuricacid. In the former case the formic acid solvent may be advantageouslyremoved by continuously passing the dispersion-treated filament througha chamber in which the air is continually exchanged, e.g. by means ofair jets and/or means for evacuation. In the latter case the sulfuricacid solvent may be advantageously removed by continuously passing thedispersion-treated filament through a water bath. After removal ofsolvent has been accomplished, the filament is dried by conventionalmeans and packaged for subsequent use.

The electrically-conductive textile fiber of the instant invention findsspecial utility in the production of fabrics the use of which avoids theaccumulation of high charges of static electricity while presenting noappreciable electrocution hazard. By way of illustration, woven fabricsare produced by standard interweaving of the electricallyconductivefiber of the instant invention with ordinary threads made from naturalfibers such as cotton or wool, and/or man-made fibers such as nylon,rayon, acrylic, or polyester. The electrically-conductive fiber ispresent in an amount equal to about 0.05-100, and preferably 0.1-5percent by weight of the woven fabric. By way of further illustratingthe special utility of the electricallyconductive fiber of the presentinvention, pile fabrics are produced comprising a backing materialhaving pile loops anchored therein. The backing material comprises chainyarns interwoven with filler yarns, as is very well-known in the art.Moreover, the backing material may be constructed from any of thematerials commonly employed in the art, such as jute or hemp, among manyothers. The pile loops comprise a yarn made of a plurality of strandstwisted together by standard techniques. At least one such strandcomprises the electrically-conductive fiber of the present invention.The balance of the yarn comprises any commonly-employed natural orman-made fibers. As will be understood by one of skill in the art, itmay not be necessary that every end of yarn in the pile contain a strandof the electrically-conductive fiber of the present invention. Moreover,more than one strand of the electrically-conductive fiber per end ofyarn in the pile may be advantageous, especially under conditions ofvery low relative humidity. In any event, the electricallyconductivefiber of the present invention is present in an amount equal to about005-100, and preferably 0.1-5 percent by weight of the pile fabric.

Fabrics such as those of the preparation of which is outlined above,when employed in an atmosphere having a relative humidity of 20%, willnot generate a static charge above about 3000 volts, which is inproximity to the threshold level of human sensitivity. These fabrics,moreover, when containing an especially preferred embodiment of theelectrically-conductive fiber of the present invention, do not presentan electrocution hazard to those contacting them in the event of anaccidental and simultaneous contact of such fabrics with a source ofessentially unlimited electrical current, as is available from anordinary electrical outlet, or an electrical appliance short-circuitedby insulation failure.

The present invention may be better understood by a reference to thefollowing illustrative examples, wherein all parts and percentages areby weight unless otherwise indicated.

Example 1 This example specifies detail concerning a method of making anelectrically-conductive fiber according to the present invention, andset forth some of the basic properties thereof.

A cold-stretched 15 denier 6 nylon monofilament having a circularcross-sectional diameter of 42p was continuously directed at a rate of400 meters/minute from a source of supply through the interface of twoopposing surfaces of a polyester pad which was kept saturated with thefollowing dispersion:

Percent Carbon black (30 III/1.) Formic acid (80%, aqueous) 90 Thereuponthe filament was conducted into and through a 20 foot-long, elongatedchamber in which the air at room temperature was continuously exchangedby means of air jets and exhaust openings. Removal of the volatileformic acid solvent was thereby accomplished, and the filament wassubstantially dry. After exiting the elongated chamber, the filament wascontinuously wound into a package at a rate of 400 meters/minute.

Microscopic examination of transverse sections of the resulting filamentrevealed a uniform dispersion of particles of carbon black in an annularregion along the length of the filament and extending prependicularlyinwardly from the periphery of the filament up to a distance equal toabout the radius of the filament. The carbon black content of thefilament was determined to be 10 percent. The total cross-sectionaldiameter of the filament, however, was not appreciably changed,measuring less than 43 A suifusion, rather than an ordinary coating, hadtherefore resulted from the specified treatment.

Conductivity measurements on the treated filament were taken using aKeithley 610 C Electrometer. Tensile properties were measured usingstandard methods and apparatus well-known in the art. The results ofthese tests are summarized in Table I below, wherein a comparison ismade with the untreated denier 6 nylon filament.

untreated (for comparlson).

The comparison in Table I shows that whereas the conductivity of thefilament according to the present invention is significantly enhanced,the tensile properties thereof are not substantially diminished; ie, thedesirable characteristics of the filamentary polymer substrate areretained while significant conductivity is achieved.

Example 2 This example specifies detail concerning a modified method ofmaking an electrically-conductive fiber according to the presentinvention.

A cold-stretched 15 denier 6 nylon monofilament having a circularcross-sectional diameter of 42 was treated in exactly the same manner asspecified in Example 1 above, except that the dispersion had thefollowing contents:

Percent Carbon black (30 m Powdered 6 nylon substrate 5 Formic acidaqueous) The powdered 6 nylon substrate was dissolved in the dispersionin order to enhance the viscosity thereof, so that even application tothe filamentary substrate might be facilitated. Moreover, the slip andflow characteristics of the dispersion were also enhanced.

Microscopic examination of transverse sections of the filament resultingfrom this procedure revealed the same annular suffusion as that of thefilament treated .according to Example 1. The total cross-sectionaldiameter of the filament remained substantially the same as that of theuntreated filament, and the annular suffusion extended perpendicularlyinwardly from the periphery of the filament up to a distance equal toabout $4 the radius of the filament. Conductivity and tensile propertieswere substantially the same as those of the treated filament ofExample 1. The carbon black content of the filament was determined to beapproximately 10 percent.

Example 3 This example specifies detail concerning yet another method ofmaking an electrically-conductive fiber according to the presentinvention.

A cold-stretched 15 denier 6 nylon monofilament identical with thoseemployed as the filamentary substrates in Examples 1 and 2 wascontinuously directed at a rate of 400 meters/minute from a source ofsupply through the interface of two opposing surfaces of a polyester padwhich was kept saturated with the following dispersion:

Percent Carbon black (30 m 9 Powdered 6 nylon polymer substrate 14Sulfuric acid (40%, aqueous) 77 The filament was then immediatelyconducted below the surface of cold water in a bath to remove sulfuricacid. After exiting the bath, the filament was dried by jets of Warm airand was finally continuously wound into a package at a rate of 400meters/minute. Examination of this filament revealed substantially thesame sulfusion as that of the treated filaments of Examples 1 and 2.Moreover, the conductivity and tensile properties of the treatedfilament of Example 3 were not appreciably different from those of thetreated filaments of Examples 1 and 2. The carbon black content of thefilament was determined to be approximately 10 percent.

Example 4 This example illustrates the integral nature of anelectrically-conductive fiber according to the present invention, andshows the surprising cohesion of polymer in the annular region ofsuffused electrically-conductive particles.

Unstretched 15 denier 6 nylon monofilament of circular cross-section wastreated exactly according to the method of Example 2. Microscopicexamination of a transverse section of the treated filament revealed asuffusion of particles of carbon black in an annular region extendingalong the entire length of the filament and perpendicularly inwardly upto a distance equal to about the radius of the filament. The resistanceof the filament was measured at 3X10 ohms/cm.

This filament was then cold stretched to 3 times its original length.The resistance of the stretched filament was measured at 5X10 ohms/cm,and close scrutiny of the surface of the stretched filament showed nodesquamation or other deterioration of the annular suffusion ofelectrically-conductive particlessubstantial loss of conductivity,excessive flaking, and overall deterioration being generally observedwhen coated filaments are subjected to such stretching operations.

Example This example further illustrates the outstanding durability ofelectrically-conductive fibers according to the present invention. Thetreated filament of Example 2 was employed in the preparation of aconventional double knit fabric using standard techniques well-known inthe art, one end of the treated filament of Example 2 being twisted inor plyed in every ten ends fed to the knitting machine. The balance ofthe fabric consisted of 1 end/ 150 denier polyester filament and 2 ends28s acrylic staple yarn. The fabric was subjected to 135 launderings[utilizing a standard laundry detergent, hot wash (120 F.) and coldrinse (wash and wear cycle)] and tumble dryings (20 minutes at anaverage temperature of 145 F.), after which the average resistance ofthe individual electrically-conductive fibers was measured. Resistancebefore launderings and tumble dryings: 5X ohms/cm. Resistance after 135launderings and tumble dryings: 5 10 ohms/cm.

Example 6 This example is illustrative of the utility of anelectrically-conductive fiber according to the present invention.Moreover, by comparison with the use of an electrically-conductive fiberof the prior art, the outstanding and unobvious advantages of fibersaccording to the present invention are further delineated.

Experiment A (This Invention) A single strand of theelectrically-conductive fiber of Example 2 above was twisted with abulked, continuous filament 6 nylon carpet yarn comprising 136individual strands and having a total denier of 2600, to produceantistatic yarn A. Employing a jute backing material and utilizing astandard tufting machine, an 18 oz./yd. level loop carpet A having apile height of A" was prepared from antistatic yarn A and a 2600/ 136bulked, continuous filament 6 nylon carpet yarn; antistatic yarn A beingincorporated in every fourth end of the pile. Theelectrically-conductive fiber of Example 2 was present in an amountequal to 0.2 percent by weight of the pile of carpet A.

Experiment B (For Comparison) An electrically-conductive fiber B,exemplary of the prior art, was prepared by coating a cold stretcheddenier monofilament of 6 nylon with a composition consisting of 25percent of a crosslinked vinyl polymer adhesive, percent ofelectrically-conductive carbon black (30 m dispersed therein, and 55percent of a methyl isobutyl ketone solvent. After the coated filamentwas passed through a slit to adjust coating thickness, it was thencompletely cured by heating with an infrared lamp. The average coatingthickness of this filament was 12 and the average electrical resistancethereof was l 10 ohms/cm. A single strand of this filament 'was thentwisted with a bulked, continuous filament 6 nylon carpet yarncomprising 136 individual strands and having a total denier of 2600, toproduce antistatic yarn B. Employing a jute backing material andutilizing a standard tufting machine, an 18 oz./yd. level loop carpet Bhaving a pile height of A" was prepared from antistatic yarn B and a2600/136 bulked, continuous filament 6 nylon carpet yarn; antistaticyarn B being incorporated in every fourth end of the pile. Theelectrically-conductive fiber B was present in an amount equal to 0.2percent by weight of the pile of carpet B.

Experiment C Carpets A and B were then individually subjected to theStatic Electricity Test set forth below. The results of such testing arereported in Table 11 below as Initial Static Electricity.

Following the initial static electricity testing, Carpets A and B wereeach subjected to an identical accelerated wearing procedure for 60hours, after which static electricity testing was again eflected. Theresults of such testing are reported in Table II below as Final StaticElectricity.

From Table II it can be seen that although carpets A and B were eachinitially static protected (viz., they did not allow the generation of astatic charge in excess of 3000 volts, which is generally accepted asthe average threshold level of human sensitivity), only carpet A wasstatic protected after extensive wear. Moreover, microscopic examinationof the electrically-conductive fibers A and B revealed that whereasfiber A showed no deterioration, the coating of fiber B was excessivelyabraded and incoherent after excessive wear.

Static Electricity Test The fabric to be tested is first cut into samplesquares 36 inches on a side. These samples are conditioned for 7 days bybeing hung from racks in a test room equipped with a rubber floor matand having an area of at least square feet, wherein the temperature iscontrolled at 70i2 F. and the relative humidity is controlled at 20%i1%.Free circulation of air over all sample surfaces is effected, but thesamples are not allowed to contact each other. A pair of Neolite orPVC-sole test shoes is also conditioned for the same period, under thesame conditions.

Residual static charge on the rubber floor mat is then neutralized bypassing twice over its entire surface a polonium wand, which consists of6 polonium 210 alloy strips mounted end-to-end on a head attached to ahandle. A fabric sample is then placed upon the rubber floor mat, andits residual static charge is neutralized in the same manner. The solesof the test shoes are then cleaned by sanding their entire surface withfine sandpaper, followed by a wiping with cheesecloth to remove dustparticles.

Wearing the test shoes and holding a hand probe which is connected to anelectrostatic detection head, a human operator steps upon the carpetsample and grounds the probe. Then While holding the hand probe, theoperator walks normally on the sample at a rate of 2 steps a second fora 30-second period, being careful not to scuff or rub the shoes over thefabric. If at the end of the 30-second period the voltage has notreached a steady maximum, the walk is continued for an additional 30seconds. The maximum voltage recorded during the walk is the staticlevel of the sample, the average for two operators being The uniquecombination of properties possessed by electrically-conductive fibersaccording to the present invention renders them especially suitable foruse not only in carpets, rugs, and other floor coverings, but also inbed coverings, especially in hospitals; in curtains, especially inhospitals for separation of cubicles; in articles of apparel, especiallyundergarments such as slips; in hosiery, especially in panty hose andhalf hose; and as sewing threads.

Although the present invention has been described in detail with respectto certain preferred embodiments thereof, it is apparent to those ofskill in the art that variations and modifications in this detail may beeffected without any departure from the spirit and scope of the presentinvention, as defined in the hereto-appended claims.

What is claimed is:

1. An electrically-conductive textile fiber comprising a filamentarypolymer substrate having finely-divided, electrically-conductiveparticles uniformly suffused as a phase independent of the polymersubstrate in an annular region located at the periphery of the filamentand extending the entire length thereof, the electrically-conductiveparticles being present in an amount sufiicient to render the electricalresistance of the textile fiber not more than about 10 ohms/cm.

2. The electrically-conductive textile fiber of claim 1, wherein thefilamentary polymer substrate is 6 nylon, and the finely-divided,electrically-conductive particles are particles of carbon black.

3. The electrically-conductive textile fiber of claim 1, wherein thefilamentary polymer substrate is of substantially cylindricalconfiguration, and the annular region of suffusedelectrically-conductive particles extends perpendicularly inwardly fromthe periphery of the filament up to a distance equal to about ,6 theradius of the filament.

4. The method of preparing an electrically conductive textile fiber froma non-conductive, filamentary polymer which comprises:

(a) applying to the filamentary polymer substrate a dispersion offinely-divided electrically-conductive particles in an amount suificientto render the electrical resistance of the textile not more than aboutohms/ cm. in a liquid which is a solvent for the substrate but does notdissolve or react with the electrically conductive particles; and

10 (b) removing the solvent from said substrate after the desired degreeof penetration has taken place in the annular region located at theperiphery of the filament and before the structural integrity of thesubstrate has been destroyed.

5. The method of claim 4, wherein the filamentary polymer substrate is 6nylon, and the finely-divided, electrically-conductive particles areparticles of carbon black.

6. The method of claim 4, wherein the filamentary polymer substrate isof substantially cylindrical configuration, and the annular region ofuniformly dispersed electrically-conductive particles is caused toextend perpendicularly inwardly from the periphery of the filament up toa distance equal to about bi the radius of the filament.

References Cited UNITED STATES PATENTS 2,473,183 6/ 1949 Watson l172762,734,978 2/1956 Bulgin 117-1 19 3,669,726 6/ 1972 Tinder ll7--2263,669,736 6/ 1972 Fujiwara l17-226 3,708,335 1/ 1973 Fujiwara 117-226LEON D. ROSDOL, Primary Examiner 'M. F. ESPOSITO, Assistant Examiner US.Cl. X.R.

